Documents DE 298 24 499 U1, U.S. Pat. No. 4,649,244 A and EP 1 164 605 B1 have disclosed electric switches of the generic type. Said switches each have a drive apparatus of the generic type in the form of an electric motor drive apparatus, with a spring energy store of the spring energy drive being latched in the tensioned state by means of a switching mechanism.
If, in the case of these switches, the latching of the spring energy store only brings with it disconnection of the electric motor drive apparatus, there is the risk of overtravel of the electric motor drive apparatus resulting in distortions in the spring energy drive. It is therefore advantageous if the latching of the spring energy store also causes the transmission of forces of the drive apparatus to the tensioning shaft to end.
In order to ensure this, in the case of the switch known from document U.S. Pat. No. 4,649,244 A, for example, a kinematic chain of the drive apparatus which connects a drive element in the form of a motor shaft to the tensioning shaft can be interrupted and closed again under the action of a control element. In this case, the interruption of the kinematic chain takes place shortly after the beginning of a latching phase, which follows on from a tensioning phase, when a predetermined first angular position of a first link, which is capable of being coupled to the tensioning shaft in a manner fixed against rotation, of the kinematic chain is reached. The kinematic chain is closed, triggered by the release of the latching of the spring energy drive, shortly after the beginning of a tension-release phase, which follows on from the latching phase, when a predetermined second angular position of this first element, which is capable of being coupled to the tensioning shaft in a manner fixed against rotation, is overshot.
In the case of the switch known from document DE 298 24 499 U1, the drive apparatus for the tensioning shaft of the spring energy drive likewise has a kinematic chain for connecting a drive element to the tensioning shaft and a control element. In this case, the control element consists of a control link arranged on the tensioning shaft in a manner fixed against rotation, an actuating lever, which rests movably on a coupling end of the tensioning shaft and is provided with ramp-like cams and an actuating slide, which is axially displaceable, is provided with mating pieces with respect to the ramp-like cams and acts on a coupling element. With this drive apparatus, a first link, which is coupled to the tensioning shaft in a manner fixed against rotation, and a second link, which is arranged coaxially with respect to the first link and is capable of rotating under the force of the drive element, of the kinematic chain are coupled to one another in a form-fitting and force-fitting manner by the coupling element. The first link is in this case formed by the coupling end of the tensioning shaft. A shaft of the electric motor drive apparatus on which the coupling element is held in a manner fixed against rotation but axially displaceable forms the second link, with the coupling element being moved under the action of the control element in the axial direction of the tensioning shaft on the second link in such a way that its coupling to the first link is eliminated when a predetermined first angular position of the first link is reached and is produced again when a predetermined second angular position of the first link is overshot.